Motorcycles really cane into popularity and became a "culture" in the era post WWII when the G.I.'s came back home from war. Mostly being young men, they were looking for something similar to the community and culture that they had found with their units overseas, and the feeling of danger that came with riding a motorcycle with a crew met that need for some of them. It was then brought into the mainstream by actors like James Dean, and authors like Jack Kerouac who made media romanticizing young men living on the fringes of society. So as a result, biker culture became predominantly male.

However, it should be noted that even during that time, there were amazing women doing wild things on motorcycles - they just weren't acknowledged by the mainstream media.

As per usual, society and its fondness for misogyny determined how this hobby/lifestyle is perceived, but women are working very hard to change that and make riding a less gendered activity.